Batch deletion is not available within the interface. We've talked about making it available after we put in an interface for recovery of deleted records. Ideally, batch modification will not be needed routinely & the use of SQL will be tolerable:
<http://wiki.refbase.net/index.php/Batch_SQL_modifications>

If you really require batch deletion, it should be easy enough to implement--we just haven't prioritized it (due to the reasons above).